• Aged ≥18 years

• Diagnosis of pathologically confirmed EG adenocarcinoma

• Diagnosis of metastatic or recurrent disease

• ECOG performance status of 0-1

• Life expectancy of ≥4 months

• Written informed consent for the study (from participant)

• Life expectancy of ≥4 months

• ECOG performance status of 0-1

• Histologic diagnosis that \& \>25% of the tumor expresses MSLN by IHC analysis. Archival tissue obtained up to 2 years before study enrollment is acceptable. IHC testing of a cell block from cytology (e.g., ascitic fluid) is acceptable if approved by the study pathologist. If adequate archival tissue is not available at screening, a fresh tumor biopsy should be obtained

• Stage IV disease with gross peritoneal carcinomatosis on imaging and/or microscopic peritoneal involvement by cytology or noted during diagnostic laparoscopy

• Disease progression or treatment intolerance after receiving at least 1 treatment regimen in the metastatic setting; patients with disease recurrence within 6 months of completing curative systemic therapy (chemotherapy, chemoradiation or adjuvant immunotherapy) are also eligible

• Patients with Her2 positive disease must have received ≥1 line of anti-Her2 based therapy

• At least 1 measurable or evaluable lesion per RECIST 1.1. Screening imaging must be obtained within 6 weeks of signing the informed consent form

• Completion of systemic therapy at least 7 days before leukapheresis

• o Immune checkpoint inhibitor therapy must be completed at least 14 days before leukapheresis

• Lab requirements (hematology):

‣ Absolute neutrophil count ≥1.0 K/mcL

⁃ Hemoglobin ≥9 gm/dL

⁃ Platelet count ≥75 K/mcL

⁃ Blood product transfusion or growth factor support cannot occur within 7 days of testing

• Lab requirements (serum chemistry):

‣ Bilirubin ≤1.5× upper limit of normal (ULN)

⁃ Serum alanine aminotransferase and serum aspartate aminotransferase (ALT/AST) level ≤3× ULN

⁃ Calculated clearance of ≥50 mL/min by Cockcroft-Gault equation

• Negative screen for infectious disease markers, including hepatitis B core antibody, hepatitis B surface antigen, hepatitis C antibody, HIV 1-2 antibody, HTLV antibody and syphilis antibody

• o Note: Patients with a history of hepatitis B virus infection are eligible if the hepatitis B viral load is undetectable. Patients with a history of hepatitis C virus infection who were treated for hepatitis C and cured are eligible if the hepatitis C viral load is undetectable

• Serum pregnancy test with negative result at screening and preconditioning and must be willing to use effective and reliable contraception for at least 12 months after T cell infusion (for female participants of childbearing age)

• Resolution of all acute toxic effects of any previous therapeutic or palliative chemotherapy, radiotherapy, or surgical procedures to grade ≤1 (CTCAE v5.0), except for neuropathy and alopecia

• Life expectancy of ≥4 months

• ECOG performance status of 0-1

• At least 1 measurable or evaluable lesion per RECIST 1.1. Screening imaging must be obtained within 4 weeks before the date of lymphodepletion

• Completion of systemic therapy at least 14 days before lymphodepleting chemotherapy

• o Immune checkpoint inhibitor therapy must be completed at least 28 days before lymphodepleting chemotherapy

• Lab requirements (hematology):

‣ Absolute neutrophil count ≥1.5 K/mcL

⁃ Hemoglobin ≥8 gm/dL

⁃ Platelet count ≥75 K/mcL

• Lab requirements (serum chemistry):

‣ Bilirubin ≤1.5× upper limit of normal (ULN)

⁃ Serum alanine aminotransferase and serum aspartate aminotransferase (ALT/AST) level ≤3× ULN

⁃ Calculated clearance of ≥50 mL/min by Cockcroft-Gault equation

• Serum pregnancy test with negative result within 7 days of planned lymphodepletion date and must be willing to use effective and reliable contraception for at least 12 months after T cell infusion (for female participants of childbearing age)

• Resolution of all acute toxic effects of any previous therapeutic or palliative chemotherapy, radiotherapy, or surgical procedures to grade ≤1 (CTCAE v5.0), except for neuropathy and alopecia

∙ Participant Exclusion Criteria